1. Field of the Invention
The present invention relates to a printer, and more particularly, it relates to a printer comprising a print head.
2. Description of the Background Art
In relation to a printer such as a thermal transfer printer, various structures are generally proposed in order to suppress reduction of print density by applying a voltage pulse (dummy pulse) to a heating element of a thermal head (print head) while performing printing on a print area. For example, Japanese Patent Laying-Open Nos. 56-161182 (1981) and 9-216398 (1997) propose such structures.
The aforementioned Japanese Patent Laying-Open No. 56-161182 describes a printer capable of suppressing reduction of print density by inhibiting the temperature of a heating element of a thermal head (print head) from decreasing below a proper level by applying a dummy pulse (voltage pulse) of an energy level causing no reaction of a thermal recording medium to the heating element also when a recording period is increased to reduce the temperature of the heating element below the proper level during printing in a print area.
The aforementioned Japanese Patent Laying-Open No. 9-216398 describes a printer, heating an ink sheet with a plurality of linear heating elements provided on a thermal head (print head) for forming dots by printing ink from portions corresponding to the heating elements onto a paper, capable of suppressing reduction of print density by applying a dummy pulse (voltage pulse) not increased to a printing temperature to the heating elements thereby increasing the temperature of the heating elements to a proper level. This printer applies the dummy pulse in line printing immediately before forming new dots when not continuously forming dots over a plurality of lines during printing in a print area.
However, while the printers described in the aforementioned Japanese Patent Laying-Open Nos. 56-161182 and 9-216398 can increase the temperatures of the heating elements to proper levels during printing, each literature neither discloses nor suggests a method of increasing the temperature(s) of the heating element(s) to a proper level when the thermal head (print head) comes into contact with the paper to reduce the temperature(s) of the heating element(s) when starting printing. When the printer applies the voltage pulse for printing to the heating element(s) of the thermal head (print head) immediately after bringing the thermal head (print head) into contact with the paper in an initial stage of printing, therefore, the temperature(s) of the heating element(s) is reduced dye to the contact with the paper, not to reach the proper level for starting printing. Therefore, print density is disadvantageously reduced in the initial stage of printing.
In this regard, a printer capable of increasing the temperature of a heating element of a thermal head (print head) to a proper level by applying a voltage pulse before starting printing (transfer) is proposed in general, as described in Japanese Patent No. 3109386, for example.
The aforementioned Japanese Patent No. 3109386 proposes a printer capable of increasing the temperature of a heating element of a thermal head (print head) to a proper level for starting transferring an overcoat material for protecting a print face to a paper by applying a voltage pulse to the heating element in a transfer area (print area) before starting the transfer operation. This printer applies the voltage pulse to the heating element by five lines without carrying the paper on a first line of the transfer area when starting transferring the overcoat material. When the technique disclosed in Japanese Patent No. 3109386 is applied to a colored ink sheet other than the overcoat material, it may conceivably possible to increase the temperature of a heating element to a proper level for starting printing by applying a voltage pulse to the heating element on a print area by five lines without carrying a paper before starting printing with the colored ink sheet.
Also when the technique disclosed in the aforementioned Japanese Patent No. 3109386 is applied to printing with a colored ink sheet, however, heat easily locally remains in the heating element of the thermal head since the printer applies the voltage pulse to the heating element without carrying the paper before starting printing. Therefore, ink of the colored ink sheet disadvantageously easily adheres to the paper due to the heat locally remaining in the heating element. Consequently, the printer must apply a large number of pulses to the heating element with a short voltage pulse width at long time intervals so that no ink adheres to the paper, and hence the time for increasing the temperature of the heating element to the proper level for starting printing is disadvantageously increased.